For example, from the following documents: GB-A-289 248, U.S. Pat. No. 2,322,715, U.S. Pat. No. 2,369,652, and U.S. Pat. No. 2,609,053, anti-torque systems for rotating wing aircraft are known that include an auxiliary rotor having an axis extending transversely relative to the fuselage of said aircraft and disposed in the vicinity of the tail end thereof. Such a tail rotor may be used not only to counterbalance the torque exerted on the fuselage by driving the main lift and propulsion rotor, but also to control the yaw of the aircraft.
Such anti-torque systems using an auxiliary rotor are particularly reliable and efficient. They are suitable for providing on a permanent basis during all stages of flight the transverse thrust required for providing the anti-torque effect and for controlling yaw. They nevertheless suffer sometimes from being heavy and noisy, and also from requiring considerable power. Nevertheless, when implemented in the most modern ways, as illustrated by document U.S. Pat. No. 4,585,391 for example, the mass, noise generated, and power required are all greatly reduced. In addition, it may be observed that when faired, an auxiliary rotor anti-torque system is entirely satisfactory with respect to safety, both in the air and on the ground.
Furthermore, the document FR-A-1 332 300 describes an anti-torque system for a rotating wing aircraft which operates by blowing, making use of the principle of a flow of air around the tail boom of the aircraft. Air under pressure flowing along the boom of the aircraft is ejected via longitudinal side slots pointing downwards and disposed vertically beneath the vertical downdraft from the rotating wing. This gives rise to a transverse aerodynamic force on said fuselage suitable for opposing the driving torque of the main lift and propulsion rotor, providing said slots are formed in the appropriate side of the fuselage.
Such anti-torque systems based on blowing are mechanically simple, however they are not efficient under certain circumstances in flight, in particular when the main rotor is not providing lift, e.g. when flying downwards, since under such circumstances, there is no longer a flow of air around the tail boom. In addition, they are also not effective when flying at high speed, since under such circumstances the forwards longitudinal speed component is much greater than the vertical component from the rotating wing, thereby cancelling the blowing effect.
In order to attempt to remedy these shortcomings of anti-torque systems based on blowing, document U.S. Pat. No. 4,200,252 provides additional means for generating a lateral jet suitable for providing an additional anti-torque force, and for enabling yaw maneuvers to be performed during all stages of flight.
Nevertheless, although the composite anti-torque system of document U.S. Pat. No. 4,200,252 provides good handling, good stability, and little sensitivity to side wind, it requires power that is not less than the power required by a high-performance anti-torque system using a faired rotor. The efficiency of the lateral jet is low. Thus, when hovering in the absence of wind, the power required is close to that required by a high-performance anti-torque system having a faired rotor. However, when the side wind is significant, the power required becomes significantly greater than that required by such a high performance anti-torque system. In addition, the mass of such a composite anti-torque system is not less than that of an anti-torque system having a faired rotor.
An object of the present invention is to provide an improved anti-torque system having a tail rotor and that makes it possible to increase the takeoff mass for a given diameter of anti-torque rotor, or for a given takeoff mass makes it possible to use a smaller diameter of anti-torque rotor, while simultaneously reducing the amount of noise generated, particularly during takeoff, landing, and hovering.